You can't make a change like momentum in a DX11 client because that is a feature of the game simulation as opposed to the game's display. Things that could be enhanced in a DX11 version could be things like models, textures, lights/shadows, particle effects, water, animations, ect.

The important thing about the DX11 client is that it won't contain any game-play changes. That means they could possibly change the way they blend animations to look like they have momentum, but they can't actually give the characters momentum.

Also, as far as character momentum goes, I always find it makes it feel like you are running on ice when you have momentum in MMOs.